Various operating procedures have been developed to reduce the hazards to workers operating in and around confined spaces. The state of the art is believed represented by the system developed by American Digital Systems, Inc. and described in detail in "ADS Field Safety Manual" by Barbara L. O'Brien, published by American Digital Systems, Inc., the text of which manual is incorporated herein by reference.
A major part of the safety equipment used in procedures described in the manual is constituted by certain well known items of mountaineering equipment including in particular mountaineer's harness, referred to in the manual as "climbing sit harness". A typical example of such harness is manufactured under the trade mark TROLL by the business of that name in Oldham, England. Although such harness serves quite well in the ADS system, it was designed for use in a rather different environment and to protect the wearer against somewhat different hazards.
Confined space work normally requires use of a two man (minimum) team, including a topside worker and a descending worker who actually enters the confined space. The duties of the topside worker include supervising the entry of the descending worker into the confined space, and breaking any accidental fall of the descending worker during entry or exit, securing the descending worker to a safe anchorage once the work zone has been reached, maintaining communication and visual contact with the descending worker, and extracting the descending worker from the confined space in the event of the latter suffering an accident or being overcome by fumes or lack of oxygen. The topside worker will often also be working in a hazardous location such as the middle of a highway. The known harness, whilst being well adapted, when sufficiently robustly constructed to stand up to continuous industrial rather than occasional recreational use, to facilitate the safety procedures required of the descending worker, is less than ideal from the point of view of the topside worker.